The present invention relates to electrical terminals and, more particularly, to male blade-type electrical plugs having angled or sloped portions or "on-ramps" formed therein to facilitate manual electrical connections with female electrical receptacles.
FIGS. 1A-1D illustrate a prior art male blade-type electrical plug, generally designated by the reference numeral 20. This type of plug is commonly used in start switches for electric motors. The male plug 20 includes a narrow tab 22 and a wide tab 24 with means for attaching an electrical conductor in the form of a pair of tabs 25 that could receive female connectors or could have conductors soldered directly thereto. The wide tab 24 has a locking hole 26 centered between opposite lateral side edges 28 and extending through the tab. As best shown in FIG. 1D (View A--A), the wide tab 24 has a tapered leading edge 30, including a beveled top edge 32 and a beveled bottom edge 34. As best shown in FIG. 1A, the tapered leading edge 30 of the wide tab 24 has diagonal corners 36. The tapered edge 30, the beveled edge 32, and the diagonal corners 36 serve to guide the tab into a female receptacle and to reduce the positional skill needed to manually connect a male plug to a female receptacle.
FIGS. 2A-2D show another prior art male blade-type electrical plug of the prior art, which is identical to the terminal illustrated in FIG. 1 except that the diagonal corners 36 depicted in FIG. 1A are replaced with rounded corners 38 to ease the connection of male terminals with female terminals. The other parts of plug are the same as those shown in FIGS. 1A-1D and are labeled with the same reference numbers followed by a prime (').
FIGS. 3A-3D illustrate a female electrical receptacle of the prior art, generally designated by the reference numeral 40, which is intended for mating with the wide tab 24, 24' of the male electrical plugs illustrated in FIGS. 1A-1D and 2A-2D. The female receptacle 40 includes a base portion 41 having a longitudinal axis 42 along its length and a lateral axis 43 along its width. The base portion further has an opposite top surface 44 and bottom surface 45, longitudinally opposite ends 46 and 47, and opposite lateral edges 48 and 49. Attached to the base portion at the lateral edges are guide rails or channels 52. The guide rails 52 slide over and embrace a wide tab 24 of a male plug as a male plug 20 and a female receptacle 40 are connected. When the wide tab 24 of the male plug 20 is inserted into the female receptacle 40, the side channels 52 of the female receptacle 40 extend around the lateral side edges 28 of the wide tab 24 to properly guide and position the tab relative to the female receptacle. of course, it is the contacting portions of the male plug and female receptacles that form the electrical connection.
As illustrated in FIGS. 3B and 3C, a typical female electrical receptacle 40 includes a resiliently bowed bridge 54 having a bump or knob 56 formed thereon. As the wide tab 24 of a male plug is inserted into a female receptacle 40, the resilient bridge 54 and the knob 56 of the female receptacle 40 are displaced by the wide tab 24 of the male plug 20 as the tab 24 is connected to the female receptacle. When the wide tab 24 of the male plug 20 is sufficiently enclosed by the side channels 52 of the female receptacle 40, the resilient bridge 54 biases the knob 56 to snap or spring into the hole 26 of the wide tab of the male plug, thereby locking the male plug and female receptacle together and ensuring an electrical connection therebetween. When a male plug 20 and female receptacle 40 are locked together in this fashion, a high extraction force, relative to the insertion force, is required to disengage the female receptacle from the wide tab 24 of the male plug 20 due to the engagement of the knob 56 of the female terminal with the locking hole 26 of the male terminal.
Ideally, male plugs and female receptacles as described above may be connected with a relatively low connection force, while disconnection requires a relatively high force due to the interaction between the bridge 54 and the knob 56 with the locking hole 26 of the tab 24 of the male plug 20. But plugs and receptacles of the prior art have failed to achieve this goal. It has been found that the required connection force of the plugs and receptacles described above is surprisingly high for assembly workers who must connect the terminals manually. Contact between the resilient bridge 54 and knob 56 of the female terminal receptacle 40 with the top surface of the wide tab 24 of the male plug 20 produces frictional forces and tight fits that significantly increase the required insertion force to engage the bridge and knob of the female receptacle with the locking hole 26 of the male plug. Small burs which may be formed on the leading edge 30 of the wide tab 24 in stamping the male plug from sheet metal, and/or burs formed during the beveling of the beveled edges 32 and 34 (See FIG. 1D) further intensify an already difficult task of connecting the plugs and receptacles, as the burs have a tendency to engage with the bridge 54 and knob 56 of the female receptacle 40 during the connection process, often with a cutting action. The combination of the bridge resistance against the wide tab of the male plug, small burs, and friction result in sticking problems that often require large forces to overcome.
The resultant magnitude of the connection force needed to connect the male plug and female receptacles has many deleterious effects. It may result in injury to the hands or wrists of manufacturing personnel, and may compromise quality control in terminal assembly operations. The large amount of force required for one to manually force the female receptacle over the wide tab of the male plug can result in the onset of carpal tunnel syndrome, and the difficulty and discomfort of forcing the female terminal over the male terminal can undesirably motivate manufacturing personnel to solve this problem in ways which compromise the electrical connection and endanger workers, such as lubricating the male and/or female terminals, and altering of the male and/or female terminals to reduce the required connection force. Beveled leading edges and diagonal or rounded corners of the male electrical plug tabs of the prior art have proven an inadequate solution to these problems.